The system studied is the ability of 8-day embryonic chick liver to exhibit adhesive recognition. (Liver cells adhere preferentially to other liver cells as opposed to a foreign cell type, i.e., neural retina cells.) The problems of isotopically labeling cells, dissociating the organs into single cell suspensions, aggregating the dissociated cells, and collecting the labeled single cell suspension by unlabeled tissue aggregates have been examined. These studies have led to a marked improvement in an assay for measuring tissue specific adhesion. The assay can now be used to probe the molecular basis for cell/cell recognition. Initial results have shown: 1) The ability of embryonic chick liver cells to adhere to liver aggregates is totally destroyed by EDTA treatment. 2) The treated cells can "repair" their own cell surface by a long term incubation in a rich medium. 3) The "repair" can be inhibited by cycloheximide but not by actinomycin D or colchicine. We are currently attempting to identify the cell surface components removed by EDTA and resynthesized during the "repair" period and to implicate these materials as responsible for cell/cell recognition and adhesion.